Air spring systems operate either with a closed or an open control loop. In the case of open air spring systems, air is drawn in from the environment by a compressor and delivered to air springs of a motor vehicle in order to raise the motor vehicle. For discharge, the air is discharged to the environment, for example. It is possible here to use a pressure reservoir to enable the motor vehicle to be raised even without the compressor, if required. In closed air spring systems, air is conveyed backwards and forwards between a pressure reservoir and the air springs in order to raise or lower the motor vehicle. Owing to leaks, it may be necessary to replenish the system with air from outside, even in a closed air spring system. The additional air can be fed into the pressure reservoir or directly into the air springs. In this system, account must be taken of the fact that the air flows under pressure through an air drier as the system is filled. During discharge, the air should be discharged to the environment through the drier in order to remove the moisture that has accumulated in the drier and regenerate the drier. German Patent DE 10 2004 038 705 B3, which is incorporated by reference herein, has disclosed a compressed air system for a motor vehicle which is used to supply air-operated loads.